Is There A Way To Join Meshes and Get Rid Of Excess Mesh?
If the excess vertices are unconnected:

In edit mode, hover your cursor over each part of the robot and press L. This will select all vertices linked to the mesh you want to save. Then Ctrl + I to inverse the selection and only select the loose mesh; press X + Enter to then delete.

If the excess vertices are connected:

In edit mode, press A to select all. Then press P and choose "separate by loose parts". The pieces will detach as you had them before as joined meshes do not necessarily join vertices (this needs to be done manually). You can then delete excess mesh before joining again. Isolating each piece by selecting it and entering local view (/) will make it easier.


If you've only just made the mistake of joining the meshes and "undo" isn't helping, look for the .blend2 file. By default, Blender saves a back-up of the last time each file was saved (for these very circumstances). You can also access the .blend2 in Info> Revert (it'll be as if you saved the file before making the mistake).